Two of the most common misconceptions about high-protein diets are that they will hurt your kidneys and that eating a lot of protein will lead to bone loss and osteoporosis. For healthy people, neither of these are true.
In fact, the evidence suggests high-protein diets can improve bone strength, and of course, eating high quality protein supports the maintenance of muscle mass as we age, which is a primary factor in bone health and the prevention of fractures related to osteoporosis.
In terms of kidney health, people with normal kidney function do not endanger their kidneys by eating a high-protein diet, but for people with risk of chronic kidney disease, high-protein diets may compromise kidney function. The relationship between kidney function and large dietary protein loads is intricate, and the following review will help you understand it and make your own decisions about protein intake.
This article will dispel the myths about high-protein eating and present five dietary strategies you should use to get the best health and body composition results out of a high-protein diet.
Protein Doesn’t Hurt Healthy Kidneys
There is no evidence that eating a high-protein diet damages healthy kidneys. The misconception that eating a lot of protein hurts the kidneys comes from the fact that in people with chronic kidney disease, high-protein intake can further compromise kidney function, but these are people whose kidneys already aren’t working well.
Kidneys do a variety of things in the body including filter your blood to get rid of waste, maintain proper blood pH, produce some hormones, and regulate the amount of water and sodium in the blood. The kidneys process the waste products of the food you eat including protein.
Eating large amounts of protein does increase the rate at which the kidneys are filtering (called hyperfiltration), but there is no evidence that this will damage them. Rather, one research group that published a review of how protein intake affects kidney function writes that “hyperfiltration is a normal adaptive mechanism” to higher protein or biological challenges. Think of it like “training” the kidneys in the same way you train the cardiovascular or muscular system with strength training.
Studies Demonstrating Safety of High-Protein Diets
Of course, strength and power athletes have been eating high-protein diets for years without developing kidney disease. A study from 2000 that used a mix of athletes, including cyclists, rowers, martial artists, and body builders, who were eating between 1.5 and 2 grams per kg of bodyweight of protein a day showed no evidence of impaired kidney function. The researchers concluded that daily protein intake as high 2.8 g/kg won’t damage the kidneys in healthy athletes.
Even in people who are “at risk” to suffer kidney disease such as diabetics or the obese—populations that already suffers from hyperfiltration of the kidneys—a high-protein diet and elevated kidney filtration doesn’t damage the kidneys. For example, a new study compared the effect of either a low-carb, high-protein diet or a low-fat weight loss diet on kidney function over two years in obese subjects.
Both diet groups lost weight, and in the high-protein diet group there was evidence of kidney hyperfiltration, but kidney function was not negatively affected in any way. Rather, kidney health was improved when the subjects lost weight because obesity alone compromises kidney function.
Even though the kidneys were working harder to filter the protein, they were working better. For example, by the end of the two-year study, the subjects had less protein in their urine, meaning the kidneys had adapted so that more of the dietary protein was absorbed and used by the body.
Pre-Existing Kidney Disease and Protein
Medical organizations discourage people with clinical kidney dysfunction or those on dialysis from eating a high protein diet.
The National Kidney Foundation has extensive recommendations with regard to protein intake for people on dialysis, but they note that these guidelines are for people on dialysis who have clinically documented kidney disease and are not intended to serve the general population or even to serve as a prevention strategy to avoid developing kidney disease.
Additional evidence that a high-protein diet may worsen pre-existing kidney disease comes from the massive Nurses’ Health Study. It included over 100,000 participants and found that those who had pre-existing kidney disease and ate large amounts of animal protein over the 11-year study period had accelerated kidney disease progression.
On the flipside, among the women in the study who had normal kidney function, there was no evidence of kidney damage or even hyperfiltration from a diet high in animal protein.
It’s reasonable to approach protein intake on an individualized basis rather than making blanket statements that eating a lot of protein will hurt the kidneys.
High Protein Diets and Bone Health
Another common misconception is that high-protein diets compromise bone health. This is not true. In fact, an analysis of 31 studies found a small but significant benefit from greater protein intake on bone health. In addition, high-protein diets were associated with more bone mineral density in several skeletal sites including the lumbar spine in every category of the population, from children to elderly men and women.
We also know that eating more protein increases levels of insulin-like growth factor I, calcium absorption, and muscle strength, all of which benefit the skeleton.
The argument that high-protein diets compromise bone strength comes from the theory that high-protein diets cause an excess acid load, which the body needs to neutralize. Some scientists theorize the body neutralizes the acid by releasing bicarbonate ions from the bone matrix, a mechanism that is accompanied by a loss of sodium, calcium, and potassium, hence the extra calcium in the urine. The excess acid load also is thought to decrease bone-building activity and increase bone loss.
It is true that an excess acid load (defined as a lower pH in the body, typically below pH of 7) is linked with bone loss and poor health in general, but simply eating a high-protein diet hasn’t proven to cause this.
This may be due to the fact that diets high in animal protein contain a lot of phosphorus, which stops the calcium loss in the urine. In contrast, purified protein sources (casein, lactalbumin, wheat gluten, dried white eggs), which don’t have the phosphorous do appear to lead to greater calcium loss in the urine and a lower pH.
Therefore, it appears there are various mechanisms that may cancel each other out from a high protein load with the end result being better bone health.
On the negative side, there’s the tendency of high-protein diets to be more acid forming and the corresponding loss of calcium in the urine. On the positive side, a high-protein diet strengthens bones by the following mechanisms:
• High-protein diets provide more vitamin D, and studies show people with higher serum vitamin D levels have less risk of bone fracture.
• Dietary protein results in greater production and action of IGF-1, a hormone that is a major regulator of bone metabolism and activates bone building. In animal studies, low-protein diets have been shown to decrease IGF-1, leading to bone loss. This effect was reversed with amino acid supplementation (greater IGF-1 levels and bone building).
• Bone building requires a pool of amino acids in the body and over 50 percent of bone is made of protein.
• Greater muscle mass, strength, and bone mass are all correlated with protein intake. It’s well known that higher protein intake alone can help maintain muscle mass as we age.
The Acid/Base Balance, Protein, and Bone Health
The real concern for maintaining bone health, regardless of protein intake, is the acid/base balance in the body, which has been shown to lead to bone and muscle loss, poor kidney function, slow metabolism and fat gain, high cortisol, and ultimately, cancer.
Called metabolic acidosis, a chronically low pH is too big of an issue to effectively address here, but the key to getting best results with a high-protein diet is to eat foods that will counter the acid from protein.
Although high-protein foods are acidic, eating them leads the body to excrete that acid more effectively, lowering your acid load.
Here are five tips on how to make a high-protein diet work for you:
1) Counter your protein acid load by eating lots of fruits and vegetables, especially dark green vegetables. Spinach, kale, zucchini, lettuce, leeks, broccoli, root vegetables, tomatoes, black currants, cherries, grapes, and kiwis are all fairly alkaline.
2) Eliminate processed grains and minimize whole grain intake because these are all more acid producing.
3) Avoid cheese (cheese is one of the most acid-producing foods), and limit dairy intake.
4) Take glutamine because it has been shown to neutralize acid in the body. Drink mineral water or add lime to water to make it more alkaline and decrease your acid load.
5) Ensure you get adequate vitamin D and magnesium because both are necessary for bone building and they enable calcium to be absorbed and used by the body. A general recommendation is up to 2,000 IUs of vitamin D and 500 mg of magnesium a day.